Mar 25, 2003 - top-level questions that can be addressed with aid of the FASTDRILL platform. Biologists are interested in investigating life in icy environ.
Eos, Vol. 84, No. 12, 25 March 2003
Workshop Advances Interdisciplinary Polar Science and Fast Ice Sheet Drilling PAGE 111 Over the last 50 years, the polar i c e sheets covering Antarctica and Greenland have b e c o m e natural scientific laboratories. Thanks to their unique environments, they yield dis coveries that advance different geophysical disciplines and capture the imagination of the general public.The scientific community inter ested in sampling polar i c e sheets and their substrata has b e e n growing recently, and now incorporates biologists, geologists, geophysicists, glaciologists,and paleo-climatologists.This multidisciplinary interest is opening new research frontiers. Significantly advancing our scientific understanding along many of these frontiers will require targeted sampling strategies and the acquisition of data from arrays of deep a c c e s s holes on spatial scales ranging from local to continent-wide. With this challenge in mind, more than 50 polar researchers and drilling engineers con vened at a workshop to discuss scientific opportunities and technological challenges of fast-access ice sheet drilling.The overarching goal of the workshop was to begin the process of matching specific drilling and sampling technologies to broad objectives of interdisci plinary polar s c i e n c e s . For convenience, the planned technological platform has b e e n dubbed FASTDRILL.A11 scientific disciplines represented at the workshop identified several top-level questions that can b e addressed with aid of the FASTDRILL platform. Biologists are interested in investigating life in icy environ ments as a potential analog for extraterrestrial life, and to better understand the origin and evolution of life on our planet. Interactions between tectonic processes and ice-sheet evolution are of primary importance to geologists and geophysicists. The glaciological community is very inter ested in the stability of modern i c e sheets and in extending the i c e c o r e record of paleo-climate further b a c k in time. Specific future applications of a FASTDRILL system may include: sampling of sub-glacial sediments and bedrock, direct investigation of ice sliding, geothermal heat flow measurements, a c c e s s to sub-glacial lakes, detection of life in deep ice through sampling and borehole logging, site selection for deep ice cores, logging climate proxies with geophysical instruments, borehole paleo-thermometry and i c e rheology studies. The multidisciplinary FASTDRILL workshop provided an opportunity to recognize the high degree of commonality in scientific objectives and targets across the different disciplines repre sented at the workshop. For instance, biologists, geologists, and glaciologists have a c o m m o n interest in sub-glacial hydrology Extremophiles, an emerging target of biological investigations, may preferentially concentrate in sub-glacial lakes and water-filled channels. Availability of sub-glacial water controls the rate of ice motion and its changes. At the same time, spatial distribution of sub-glacial water production is largely determined by geothermal heat flux, a quantity of primary importance in interpretations of sub-glacial geology Hence,
borehole surveys of regional- or continental-scale variability in geothermal heat flux and subglacial hydrology would provide key observa tional constraints on top-level scientific questions posed by several different disciplines. Another excellent example of a multidisci plinary FASTDRILL target of great importance would b e the search for old ice (~1 m.y?). Discovery of such old ice would have obvious significance for ice-core paleo-climatology It would also provide biologic material for investigating long-term microbial survivability in ice. Specific geographic locations that were frequently mentioned as possible targets of multidisciplinary fast-access drilling included the West Antarctic Ice Sheet, Lake Vostok, the Gamburtsev Mountains, and putative sub-glacial volcanoes in West Antarctica and Greenland. Workshop participants put considerable effort into defining the technological parameters of a FASTDRILL that would satisfy the discussed scientific goals. Such a drill would have to b e easily deployable, fast, and mobile, so that several deep boreholes (1-4 km) could be accomplished within o n e season along a transect with a length of up to hundreds of kilometers. This implies portability of drilling and sampling equipment on a transport plane (LC-130) and on sleds. Rapid recovery of short, - 1 0 m cores of ice, sub-glacial sediment, and bedrock, as well as acquisition of sub^lacial water samples, must b e possible. Also of great importance is the ability to perform geophysical borehole logging and to install long-term geophysical observatories— for example, seismometers—in ice and beneath i c e , < 1 0 m beneath the ice base. Borehole diameters can b e narrow for some applications, such as borehole logging, but they should b e as large as possible for core recovery and deployment of remotely operated vehicles in sub-glacial water bodies. Many participants expressed interest in having directional drilling capabilities with a horizontal reach of up to a few kilometers.This would permit acquisition of multiple samples or cores along a horizontal transect without having to drill multiple deep access holes. In addition, some important targets— for example, shear margins of fast ice streams— cannot be accessed with strictly vertical boreholes because of the high density of surface crevasses. Directional drilling may provide a solution to this problem. All of the drilling and sampling equipment should b e engineered to work at low temperatures (down to - 5 0 ° C ) . Safety and environmental c o n c e r n s related to fast i c e sheet drilling figured prominently in workshop discussions focused on technology issues. Whenever heavy and complicated drill rigs are deployed, there is the danger of physical injury. Researchers accessing sub-glacial sedi mentary basins could encounter pressurized natural gas. In addition, drilling into large subglacial lakes may trigger depressurization and catastrophic degassing of water. Finally, subglacial environments are pristine and fragile, and the top priority should b e to avoid con taminating them with drilling fluids. Fortunately, in many of the proposed appli cations of i c e sheet drilling, clean hot water
would b e the drilling fluid of choice. Only in a few specific cases, more traditional drilling fluids must b e used, such as butyl a c e t a t e for optical borehole logging.The preferred strategy then, would b e to pump the fluid out of the b o r e h o l e and replace it with water before abandoning the site. Drilling engineers from a c a d e m i a and industry provided crucial feed b a c k on the availability and known capabilities of relevant drilling and sampling/coring tech nologies. Three main alternatives for drilling were considered: hot-water ice drilling, wire-line rotary drilling, and coiled-tube drilling (CTD). Hot-water ice drills are used widely for making shallow,
